Subgingival adherent plaque, composed mainly of Gram (positive) microorganisms adjacent to the cementum, and subgingival loosely adherent plaque, composed mainly of Gram (negative) microorganisms adjacent to the sulcular epithelium, may exert a bidirectional destructive effect on these tissues. Hydroxyapatite-durcupan strips and cemental strips (prepared from extracted normal teeth) will be placed subgingivally for varying lengths of time in patients having chronic or juvenile periodontitis, and removed at the time of therapeutically required surgery. In conjunction with the removal of hydroxyapatite strips, samples of adjacent sulcular tissue will also be obtained. These strips and the sulcular tissue will be processed together for stereomorphometric assessment of plaque microorganisms and epithelial alterations. The effects of plaque accumulation on epithelial samples will also be tested by in vitro permeability assay. Cemental strips will be evaluated by testing the permeability of these strips to dyes and markers, and by SEM and TEM determination of the extent of cemental demineralization and calculus deposition. The disease entities chosen for study, the techniques for sample collection, and the methods proposed for analysis of those samples will, it is believed, elucidate the bidirectional effects of subgingival plaque.